Shell catalyst, a process for its production and its use

ABSTRACT

The invention is an improved palladium-containing catalyst and process for preparing the catalyst. The catalyst is prepared by impregnating a dry activated carbon with a pH above 8 with a solution of palladium salt, separating the aqueous phase from the impregnated activated carbon when the aqueous phase has reached a pH of at least 1 and reducing the palladium which is supported on the activated carbon.

FIELD OF THE INVENTION

This invention relates to a shell catalyst containing 0.3 to 5% byweight and, more particularly, 0.5 to 2% by weight of palladium on anactive carbon support, based on the dried catalyst, obtainable byimpregnation of the support with an aqueous palladium salt solution,precipitation of palladium and reduction (activation).

BACKGROUND OF THE INVENTION

The hardening of unsaturated fats, oils and fatty acids on an industrialscale by hydrogenation is carried out with nickel catalysts in the formof fine powders in intensively stirred autoclaves under hydrogenpressures of up to 20 bar and at temperatures of up to 250° C.Particular problems arise above all in the hydrogenation of fatty acids.On the one hand, nickel soaps are formed at the temperatures mentionedand can only be removed from the product by distillation. In addition,the activity and life of the catalyst are reduced through the dissolvingout of nickel from the catalyst. On the other hand, separation of thecatalyst from the product is complicated and leads to increased lossesof product.

These disadvantages can be avoided by using palladium catalysts.Palladium is acid-resistant. Accordingly, no soaps requiring separationare formed. The life of such a catalyst is thus so long thateconomically justifiable continuous hydrogenation in a fixed catalystbed is possible. Accordingly, there is no longer any need for thecomplicated separation of the catalyst from the product.

In addition, palladium catalysts are eminently suitable for thehydrogenation of edible fats because the hydrogenated product containsno residual nickel at all.

RELATED ART

A catalyst of the type mentioned at the beginning is known fromCA-B-1,157,844. As described in detail in this document with referencesfrom the patent literature, the production of a supported noble-metalcatalyst generally consists of the three steps of impregnation,precipitation and reduction. For example, this document citesGB-B-799,871 in which a support material is impregnated with PdCl₂solution and is precipitated with NaHCO₃ as Pd(OH)₂.

Similar processes are described in U.S. Pat. No. 2,749,359, U.S. Pat.No. 3,736,266 and DE 28 50 510.

According to CA-B-1,157,844, the activity of the palladium catalyst isincreased by first charging a catalyst support of extruded active carbonwith water or an organic liquid before it is impregnated with thepalladium salt solution. In this way, the noble metal is only applied tothe support in an outer shell. After an impregnation time of 1 hour, thepH value is adjusted to around 4.0 by addition of sodium hydroxidesolution so that palladium precipitates as hydroxide. The production ofthe catalyst is completed by filtration, washing, drying and reduction.

The problem addressed by the present invention was to provide a catalystof the type mentioned at the beginning which would combine considerablyhigher activity with a longer life. In addition, the invention set outto provide a simpler and more economical process for the production ofsuch a catalyst.

BRIEF SUMMARY OF THE INVENTION

According to the invention, the solution to this problem ischaracterized in that active carbon showing an alkaline reaction, moreparticularly with a pH value of at least 8, is impregnated with thepalladium salt solution and the supernatant liquid is separated offafter it has reached a pH value of at least 1, more particularly atleast 3 and preferably at least 4.

It has surprisingly been found that particularly active catalysts with avery long life are obtained if the basicity present in the carbon issufficient to increase the pH value of the noble metal salt solutionafter impregnation to a minimum level which is sufficient forprecipitation. In this case, all the palladium contained in the solutionis precipitated in a peripheral zone of the support. The supernatantsolution is palladium-free, so that there is no need to add an alkali,for example sodium hydroxide, to complete the precipitation process. Ashell-type impregnation is obtained, the concentration of noble metalfalling to almost zero in an approximately 0.2 mm peripheral zone, asshown by physical surface analysis.

DETAILED DESCRIPTION OF THE INVENTION

Alkali metal tetrahalopalladates, for example, may be used as thepalladium salt, although palladium chloride, palladium nitrate and otherpalladium salts are also suitable.

The iodine values obtainable where hydrogenation is carried out with thecatalyst according to the invention are distinctly lower than thoseobtained where the catalyst described in CA-B-1,157,844 is used forcomparable hydrogenation conditions. Thus, according to Example 10 ofthis document, an iodine value of only 1.7 is reached for a liquidthroughput per catalyst volume and time (LHSV) of only 0.2 l/h (2.5 l ofcatalyst and 0.625 l/h throughput of palm kernel oil) and a pressure of25 bar. By contrast, palm kernel oil can be hydrogenated to iodinevalues below 0.6 with the catalyst according to the invention for anLHSV of around l/h.

Whereas the catalyst described in CA-B-1,157,844 in the test withdistilled tallow fatty acid - only reaches iodine values below 1 for avery low liquid throughput of 0.2 l/h, the iodine value rising to2.5-3.3 when the load is increased to only 0.6 l/h, it is possible withthe catalyst according to the invention to reach an iodine value below0.5 for loads of 1/h and an iodine value still well below 1 for loadsfor 2 to 3/h (Example 5).

According to CA-B-1,157,844, the specific palladium consumption is0.00089%. The corresponding value from Example 5 after 2,429 kg of fattyacids have been hydrogenated with 1 l of catalyst--still with nosignificant reduction in activity--is 0.00041% and is thus 50% below thecomparison value.

The catalyst according to the invention can be produced particularlysimply and economically if the volume of the salt solution issubstantially equal to the total pore volume of the active carbon. Theactive carbon support can then be impregnated by spraying with thesolution.

According to the invention, there is no need for the catalyst to beprecharged with liquid before impregnation. Accordingly, the activecarbon is preferably contacted with the salt solution in dry form. Inspite of this, an excellent shell impregnation of the noble metal isobtained in this way, as described in Example 2.

In another embodiment of the invention, the active carbon is agitatedduring addition of the solution.

In addition, to obtain a low-halide catalyst, the product obtainedshould be filtered off and washed with water after impregnation withpalladium halide salts.

The present invention also relates to a process for the production ofthis catalyst and to a process for the hardening of fats, oils, fattyacid esters, other fatty acid derivatives and, in particular, free fattyacids by catalytic hydrogenation with hydrogen. The hydrogenation ispreferably carried out at temperatures of 80° C. to 250° C. underabsolute pressures of 0.5 to 50 bar. The hydrogenation may optionally becarried out in such a way that the iodine value after the reaction is aslow as possible, as is generally necessary in the hydrogenation of fattyacids for industrial applications, but which can also be desirable inthe hydrogenation of methyl esters (Example 8, 18) or neutral oils(Example 15). These reactions are generally carried out under a hydrogenpressure of 20 bar. However, it is also possible selectively tohydrogenate starting materials with high iodine values under definedconditions to certain iodine values in order to establish certainperformance properties. In this case, parameters (temperature, pressure)differing from the normal conditions have to be established. Thisso-called partial hardening is described in Example 12 for the hardeningof rapeseed oil fatty acid and in Example 16 for the hardening ofsunflower oil and rape seed oil.

In another embodiment of the invention intended in particular for thehardening of fatty acids, distilled fatty acids are used because theircolor is so greatly improved during hardening that the color requiredfor marketable products is achieved without any need for the otherwiseusual aftertreatment by adsorption.

The invention is illustrated by the following Examples and test resultsin conjunction with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the distribution of palladium over the layer thickness of acatalyst according to the invention.

FIG. 2 shows the results of a long-term test in the form of a graph inwhich the residual iodine value, the liquid load (LHSV), the temperatureand the acid value are plotted against the overall throughput.

FIG. 3 is a flow chart of a pilot plant for the continuous hydrogenationof fatty acids.

EXAMPLES Example 1

Production of the catalyst

2 ml of HCl (conc.) and 2.21 g of NaCl were added to and stirred with asuspension of 3.342 g of PdCl₂ in 160 ml of water until a clear solutionwas formed. The solution thus formed was added while shaking at roomtemperature to 100 g of active carbon (Cecarbon GAC 30, sieve fractionlarger than 1.4 mm) in a 500 ml flask. The active carbon had a BETsurface of 1,140 m² /g, a pore volume of 0.32 ml/g, as measured by Hgporosimetry, a pH value of 8.3 (10% in water) and a residue on ignitionof 13.4%. The solution was spontaneously decolored and the pH value ofthe supernatant solution rose from below 1 to around 3. The mixture wasleft standing for 1 h, the pH value rising to 4-5. The supernatantsolution was then filtered off and washed substantially free fromchloride with 2 l of water. The catalyst was dried first by suction andthen overnight at 120° C. Yield: 96.2 g (dry).

Example 2

Production of the catalyst

1,680 g of a solution of Na₂ PdCl₄ (Pd content 20 g) were added at roomtemperature to 1,000 g of the same active carbon granules as in Example1 (Cecarbon GAC 30) in a plowshare mixer with the mixer running. Afterstanding for a short time, the granules were rinsed with a little waterfrom the mixer and then left to react for 1 hour in a glass beaker. Thecatalyst was washed twice with 10 l of water until it was substantiallyfree from chloride and then dried first by suction and then at 120° C.Yield: 1,051.5 g.

Noble metal distribution:

The distribution of palladium in a particle of the catalyst according toExample 2 was determined by energydispersive X-ray microanalysis. Theresults are shown in FIG. 1. The concentration of palladium at thesurface of the particle was arbitrarily set at 1 and the concentrationinside the catalyst particle was determined in relation to that value.It can clearly be seen that the concentration of palladium has fallen to10% at a distance of only 200 μm from the surface.

Example 3

Production of the catalyst

In a paddle mixer with a total volume of around 20 l, 3,595 g of Pdsolution (Na₂ PdCl₄, 100 g Pd) and 1,400 g of distilled water were runat room temperature into 5,000 g of active carbon granules (Cecarbon GAC30, sieve fraction 1.2 to 3.0 mm) with the mixer running. The mixer wasthen stopped and its contents were drained off and rinsed with 2 litersof distilled water. 1 Liter of water was then added so that the carbonwas covered with liquid. After 1 hour, the whole was filtered undersuction through a filter nutsch. 6.5 l of filtrate with a pH value of4.5 were obtained. The filtrate was then washed five times with 10 l ofwater so that it only contained small quantities of chloride ions. Thecatalyst was dried at 120° C. Another two batches were produced in thesame way so that a total of 15 kg of catalyst with an overall volume ofaround 30 l was available.

Activation:

For activation before use, all the catalysts produced in the Exampleswere reduced. To this end, they were heated for 4 h to 200° C. in astream of nitrogen of 1 Nm³ /h. 50 Nl/h of hydrogen were then added tothe nitrogen over a period of 20 h at 200° C. The temperature was thenmaintained for 2 h in an atmosphere of pure hydrogen before the catalystwas used for hydrogenation.

Example 4

Use of the catalyst of Example 1.

The catalyst produced in accordance with Example 1 was tested in alaboratory hydrogenation reactor. A shaft reactor with a catalyst volumeof 150 ml (catalyst filling 66.6 g) was charged with liquid and gaseousphase in co-current flow. All the tests were carried out under ahydrogen pressure of 20 bar. Distilled and crude tallow fatty acid wereused as raw materials for hardening. The throughput, LHSV andtemperature T were varied within wide limits. Individual results are setout in Table 1. It can clearly be seen that the catalyst is highlyactive even at low temperatures (150° C., LHSV=1, iodine value IV=0.46)and is capable of withstanding very high loads at high temperatures(200° C., LHSV=3.2, IV=0.75). Under all conditions, the catalyst ishighly selective, i.e. there are no unwanted secondary reactions whichwould be reflected in a reduction in the acid value AV.

                  TABLE 1                                                         ______________________________________                                        Hydrogenation results                                                                  T/°C.                                                                       LHSV                   Conversion                                        (°C.)                                                                       (l/h)    IV      AV    (%)                                      ______________________________________                                        Distilled tallow                                                                         200    1.07     0.11  202.3 99.8                                   fatty acid 200    1.00     0.13  203.3 99.8                                   Iodine value 54.2                                                                        200    2.00     0.22  204.0 99.6                                              200    2.13     0.25  203.6 99.5                                              201    3.20     0.75  203.6 98.6                                              171    3.13     1.33  204.4 97.5                                              170    2.00     0.59  203.5 98.9                                              171    2.00     0.75  204.4 98.6                                              170    1.00     0.28  204.7 99.5                                              170    0.93     0.29  204.7 99.5                                              151    1.00     0.46  204.2 99.2                                              150    2.07     3.18  204.3 94.1                                   Crude tallow                                                                             171    1.07     5.34  185.9 90.4                                   fatty acid 170    1.00     5.21  186.1 90.6                                   Iodine value 55.4                                                                        200    1.00     2.26  186.9 95.3                                              200    0.93     2.05  189.3 96.3                                              220    0.93     0.90  190.3 98.4                                   ______________________________________                                    

Example 5

Use of the catalyst of Example 2

The catalyst produced in accordance with Example 2 was subjected to along-term test. To this end, 500 g (1 liter) of the catalyst were testedfor 116 days under hydrogenating conditions (hydrogen pressure 20 bar)in a pilot plant with various fatty acids, mainly distilled tallow fattyacid. The throughput and temperature were varied within wide limits. Itwas found that, even after this long period and a quantity of rawmaterial corresponding to 4,858 kg of product/kg of catalyst, there wasstill no significant reduction in the activity of the catalyst (IV below0.5 for LHSV=1 and a temperature of 190° C.). Results covering theentire test period are shown in the form of a graph in FIG. 2. Theiodine value and LHSV and the temperature and acid values can be readoff from the same scales. The increase in the iodine value on the leftof the graph is attributable to the use of crude fatty acid.

Example 6

Use of the catalyst of Example 3.

Hydrogenation tests were carried out on a semi-industrial scale with13.2 kg of the catalyst produced in accordance with Example 3. The plantwas a recycle gas plant in which the hydrogen used in excess isseparated from the product and recirculated (FIG. 3).

Fatty acid 1 is pumped together with the recycle gas into a reactor 4via a receiver 2 and a heater 3. The hydrogenated product separated inthe high-pressure separator 5 collects in a receiver 6. From the recyclegas compressor 7, the excess hydrogen and also fresh hydrogen 8 arereturned to the heater 3.

The test parameters are set out in Table 2.

                  TABLE 2                                                         ______________________________________                                        Test parameters                                                               ______________________________________                                        Reactor type:       single tube                                               Diameter:           63 mm                                                     Length of catalyst bed:                                                                           8,000 mm                                                  Volume of catalyst bed:                                                                           25 l                                                      L/D:                127:1                                                     Pressure:           20 bar                                                    Recycle gas volume: 1.4-1.8 Nm.sup.3 /l cat · h                      Throughput:         1 m.sup.3 /m.sup.3 cat · h                       Liquid load:        8 m.sup.3 /m.sup.3 · h                           Gas load (190° C.):                                                                        950-1220 m.sup.3 /m.sup.2 · h                    ______________________________________                                    

Various fatty acid qualities were tested, particularly in regard to thecolor of the products. The average values of the results obtained forthe individual products are set out in Tables 3 and 4. It can be seen inparticular from Table 4 that the color of the products is distinctlyimproved by the hydrogenation step.

                                      TABLE 3                                     __________________________________________________________________________                   Iodine                                                                        value                                                                              IV  AV  Saponification                                                                        Unsaponifiables                                                                        Unsaponifiables                                 before                                                                             after                                                                             after                                                                             value SV                                                                              (UV)     (UV) before                      Material       hydr.                                                                              hydr.                                                                             hydr.                                                                             after hydr.                                                                           after hydr.                                                                            hydrogenation                    __________________________________________________________________________    1  Tallow fatty acid                                                                         58.1 0.6 205.2                                                                             205.3   0.6%     --                               2  Tallow fatty acid                                                                         58.0 0.4 205.1                                                                             205.2   0.4%     0.5%                             3  Tallow fatty acid                                                                         61.3 0.2 204.8                                                                             205.1   0.3%     0.4%                             4  Tallow fatty acid                                                                         58.7 0.3 205.1                                                                             205.4                                             5  Separated stearin                                                                         13.2 0.2 208.4                                                                             208.5   0.5%     0.4%                                (from tallow fatty acid)                                                   6  Separated stearin                                                                         22.2 0.4 208.7                                                                             209.1   0.5      --                                  (from tallow fatty acid)                                                   7  Separated stearin                                                                         21.8 0.3 209.1                                                                             209.2   0.5      --                                  (from tallow fatty acid)                                                   8  Separated stearin                                                                         21.3 0.2 208.5                                                                             208.9                                                (from tallow fatty acid)                                                   9  Separated stearin                                                                         20.2 0.2 208.5                                                    (from tallow fatty acid)                                                   10 Tallow fatty acid                                                                         59.8 0.2 203.8                                                 11 Separated stearin                                                                         18.5 0.1 209.1                                                    (containing oleic acid)                                                    __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                        Color characteristics (Lovibond 51/4")                                                         Before      After                                                             hydrogenation                                                                             hydrogenation                                                     (yellow value/                                                                            (yellow value/                                   Material         red value)  red value)                                       ______________________________________                                        1    Tallow fatty acid           1.7/0.7                                      2    Tallow fatty acid                                                                             13.0/2.0    1.6/0.6                                      3    Tallow fatty acid                                                                             3.5/0.8     0.5/0.3                                      4    Tallow fatty acid                                                                             2.4/0.6     0.1/0.1                                      5    Separated stearin                                                                             2.0/0.5     0.6/0.4                                           (from tallow fatty acid)                                                 6    Separated stearin                                                                             7.7/1.4     2.8/1.0                                           (from tallow fatty acid)                                                 7    Separated stearin                                                                             2.9/0.6     1.6/0.7                                           (from tallow fatty acid)                                                 8    Separated stearin                                                                             7.7/1.5     1.8/0.8                                           (from tallow fatty acid)                                                 9    Separated stearin                                                                             5.7/1.3     1.9/0.9                                           (from tallow fatty acid)                                                 10   Tallow fatty acid                                                                             2.4/0.5     0.7/0.3                                      11   Separated stearin                                                                             1.7/0.4     0.8/0.5                                           (containing oleic acid)                                                  ______________________________________                                    

Example 7

Production of the catalyst

716.2 g of extruded active carbon (Carbotech A35/2, 2 mm extrudate, BETsurface 890 m² /g, Hg pore volume 0.74 ml/g, pH value 8.7 (10% in H₂ O)were mixed at room temperature with 514.7 g of Pd salt solution (14.32 gof Pd as Na₂ PdCl₄) and 200 g of H₂ O. Another 1,000 g of water werethen added. After 1 hour, the mixture was filtered off under suctionthrough a filter nutsch and washed with 17 l of water untilsubstantially free from chloride. The catalyst was dried overnight at120° C. Yield: 717.5 g.

Example 8

Use of the catalyst of Example 7

355 g (corresponding to 1 l) of the catalyst of Example 7 wereactivity-tested for 18 days in a hydrogenation reactor using various rawmaterials. After activation in the usual way (as described above), thecatalyst was charged with 171 l of tallow ethyl ester (Me-Ti; IV =50.2;AV=0.80; SV=199.5) and 218 l of tallow fatty acid (Ti-FA; IV=58.5;AV=206.3). The following hydrogenation results were obtained:

    ______________________________________                                                 Total     Temperature                                                         throughput                                                                              heating circuit                                                                           LHSV                                           Raw material                                                                           (l)       (°C.)                                                                              (l/h)  IV                                      ______________________________________                                        Me--Ti   38        170         1      0.07                                             86        170         1      0.06                                             110       180         2      0.11                                             123       180         2      0.11                                    Ti-FA    197       190         1      0.26                                             256       190         1      0.21                                             357       200         1      0.20                                             389       200         1      0.22                                    ______________________________________                                    

Example 9

Production of the catalyst

1,000 g of CECARBON GAC 616G active carbon granules with a particlessize of 1.2 to 3.4 mm and an apparent density of 0.51 kg/l (pH value7.8; BET surface 1,190 m² /g and Hg pore volume 0.15 ml/g) wereintroduced into a mixing vessel.

718.9 g of a solution of Na₂ PdCl₄ (corresponding to 20.0 g ofpalladium) were combined with 281 g of H₂ O and added as described tothe carbon support. The mixture was then diluted with 667 g of H₂ O toestablish the same liquid ratios. After 1 hour, the catalyst wasfiltered in the usual way and washed until substantially free fromchloride.

The pH value of the first filtrate was 3.5. After the washing step, thewashing water had a pH value of 5.5. The moist granules were dried at120° C.

Example 10

Use of the catalyst of Example 9

520 g (corresponding to 1,000 ml) of the catalyst produced in accordancewith Example 9 were tested for 36 days in a 1.2 liter hydrogenationreactor with a total of 660 l of raw materials of various kinds (ediblebeef tallow: IV=46.6; AV=2.70; SV=195; bone fatty acid: IV=60.6;AV=205.7; tallow fatty acid: IV=58.5, SV 206.3; tallow methyl ester:IV=48.9, AV=0.40, SV=195).

The following hydrogenation results were obtained:

    ______________________________________                                                   Total                                                                         throughput                                                                              Temperature                                                                              LHSV                                          Raw material                                                                             (l)       (°C.)                                                                             (l/h)  IV                                     ______________________________________                                        Beef tallow                                                                              17        160        1      4.0                                               33        200        1      1.1                                               65        220        1      0.57                                              106       220        0.5    0.13                                              154       200        0.5    0.26                                              173       200        0.5    0.42                                   Bone fatty acid                                                                          189       200        1      0.07                                              222       200        1      0.10                                   Tallow fatty acid                                                                        278       200        1      0.31                                   Tallow methyl ester                                                                      394       200        1      0.10                                   Tallow fatty acid                                                                        512       200        1      0.29                                   Tallow methyl ester                                                                      532       200        1      0.07                                              660       190        1      0.12                                   ______________________________________                                    

Example 11

Production of the catalyst (1% Pd/C)

1,500 g of CECARBON GAC 30 active carbon granules with a particle sizeof 1.3 to 3 mm and an apparent density of 0.49 kg/l (pH value 8.3 (10%in H₂ O) ; BET surface 1,140 m² /g and Hg pore volume 0.32 ml/g) wereintroduced into a mixing vessel, after which a solution of 539.2 g ofNa₂ PdCl₄ (corresponding to 15.0 g of palladium) in 961 g of H₂ O, i.e.1,500 g of solution, was rapidly added with stirring. Another 1,000 g ofH₂ O were then added to obtain a supernatant liquid phase. Afterstanding for 1 hour, the impregnated supported catalyst was filtered offfrom the salt solution. The catalyst was then washed with 30 l of wateruntil substantially free from chloride, dried at 120° C. and used forhydrogenation tests.

Example 12

Use of the catalyst of Example 11

495 g corresponding to 1,000 ml of the catalyst produced in accordancewith Example 11 were tested in a hydrogenation reactor for 51 days witha total of 1,500 l of various raw materials:

    ______________________________________                                        Separated stearin                                                                             IV = 18.4 AV = 209.0                                          Tallow fatty acid                                                                             IV = 57.4 AV = 205.7                                          Bone fatty acid IV = 60.6 AV = 205.7                                          Rapeseed oil fatty acid                                                                        IV = 115.8                                                                             AV = 200.9                                          ______________________________________                                    

The rapeseed oil fatty acid was hydrogenated at various temperatures andpressures to establish specific iodine values. The other raw materialswere hydrogenated in the usual way at a constant hydrogen pressure of 20bar.

The following hydrogenation results were obtained:

    ______________________________________                                                  Total                                                                         throughput                                                                              T       P     LHSV                                        Raw material                                                                            (l)       (°C.)                                                                          (bar) (l/h)  IV                                   ______________________________________                                        Separated stearin                                                                       7         160     20.7  1      0.03                                           49        160     20.8  2      0.67                                 Tallow fatty acid                                                                       78        160     19.8  1      0.36                                           123       180     20.0  1      0.46                                           194       200     21.2  1      0.39                                           276       200     19.9  1      0.17                                 Bone fatty acid                                                                         434       210     20.1  2      0.19                                           706       210     20.1  2      0.17                                           892       210     20.4  2      0.20                                 Rapeseed oil fatty                                                                      938       80      20.4  2      83.6                                 acid      967       80      10.4  1      82.8                                           991       90      5.6   1      81.1                                           1087      90      5.5   1      82.0                                           1111      100     4.8   1      67.5                                           1135      105     5.3   1      57.9                                           1159      110     5.3   1      49.6                                           1183      110     5.2   1      49.5                                 Bone fatty acid                                                                         1253      210     20.4  2      0.50                                           1377      210     20.0  1      0.18                                           1409      210     20.3  1      0.09                                 Tallow fatty acid                                                                       1500      210     19.8  1      0.73                                 ______________________________________                                    

Example 13

Production of the catalyst (0.5% Pd/C)

1,500 g of GAC 30 active carbon granules with a particle size of 1.3 to3 mm (apparent density 0.49 kg/l; pH value 8.3; BET surface 1,140 m² /gand Hg pore volume 0.32 ml/g) were introduced into a mixing vessel.

269.6 g of Pd salt solution as Na₂ PdCl₄ (corresponding to 7.5 g of Pd)were combined with 1,230 g of H₂ O and mixed with the carbon granules,followed by washing with 1,000 g of H₂ O. The catalyst granules werethen washed as in Example 11 until substantially free from chloride andsubsequently dried at 120° C.

Example 14

Use of the catalyst of Example 13

525 g (corresponding to 1,000 ml) of the catalyst produced in accordancewith Example 13 were tested for 17 days in a hydrogenation reactor usinga total of 369 l of raw materials. The following raw materials wereused:

    ______________________________________                                        Tallow fatty acid                                                                             IV = 58.5                                                                              AV = 206.3                                           Bone fatty acid IV = 60.6                                                                              AV = 205.7                                           ______________________________________                                    

The following hydrogenation results were obtained:

    ______________________________________                                                   Total                                                                         throughput                                                                              Temperature                                                                              LHSV                                          Raw material                                                                             (1)       (°C.)                                                                             (l/h)  IV                                     ______________________________________                                        Tallow fatty acid                                                                        24        190        1      0.87                                              48        210        1      0.41                                              87        210        1      0.88                                              169       220        1      0.59                                              240       220        1      0.61                                   Bone fatty acid                                                                          353       220        1      0.19                                              369       220        1      0.13                                   ______________________________________                                    

Example 15

Production of the catalyst

1,500 g of GAC 30 active carbon granules with a particle size of 1.2 to3.4 mm and an apparent density of 0.51 (pH value 7.8; BET surface 1,190m² /g; Hg pore volume 0.15 ml/g) were introduced into a mixing vessel.

1,078.4 g of Pd salt solution as Na₂ PdCl₄ (corresponding to 30.0 g ofpalladium) were combined with 421.6 g of H₂ O and added to the carbongranules. Another 1,000 g of H₂ O were then added and, after standing,the product obtained was worked up as described above.

The first filtrate had a pH value of 2.8 and the final washing water apH value of 4.2.

Example 16

Hydrogenation tests

527 g (corresponding to 1,000 ml) of the catalyst produced in accordancewith Example 15 were tested for 55 days in a hydrogenation reactor usinga total of 1,172 l of various raw materials, namely:

    ______________________________________                                        Palm kernel oil, ref. (PK)                                                                     IV = 17.4   SV = 244                                         Sunflower oil (SF oil), new                                                                    IV = 80.7   SV = 189                                         Rapeseed oil, ref.                                                                             IV = 112.6  SV = 192                                         Separated stearin St20                                                                         IV = 20     AV = 208.6                                       Tallow fatty acid (TiFA)                                                                       IV = 50     AV = 206.3                                       ______________________________________                                    

The three triglycerides were used first. Of these, the sunflower oil andrapeseed oil were only selectively hydrogenated, i.e. the iodine valuewas reduced to a certain average value. All the tests were carried outunder a hydrogen pressure of 20 bar. The following results wereobtained:

    ______________________________________                                                     Total                                                                         throughput                                                                             T        LHSV                                           Raw material (l)      (°C.)                                                                           (l/h) IV                                       ______________________________________                                        PK oil       54       180      1     0.28                                                  118      190      1     0.38                                                  166      190      1     0.57                                     SF oil, new  182      190      1     7.3                                                   200      200      0.5   2.1                                                   216      150      1.0   27.3                                                  232      150      1.0   35.6                                                  304      135      1.0   56.1                                     Rapeseed oil, ref.                                                                         337      135      1.0   83.4                                                  378      150      1.0   74.4                                                  402      165      1.0   65.8                                                  425      190      1.0   48.8                                                  519      230      0.5   6.5                                      St20         549      200      1.0   0.1                                                   800      200      1.0   0.1                                      TiFA         845      200      1.0   0.1                                                   1084     200      1.0   0.1                                      ______________________________________                                    

Example 17

Production of the catalyst (2% Pd/C)

716.2 g of active carbon (Carbotech A35/2, 1 mm extrudate with anapparent density of 0.36 kg/l, a BET surface of 892 mm² /g and an Hgpore volume of 0.74 ml/g) were introduced into a mixing vessel and mixedwhile stirring with 514.7 g of a solution of Na₂ PdCl₄ (corresponding to14.3 g of palladium) and 200 g of water.

Another 1,000 g of water were then added and, after standing for 1 hour,the mixture was filtered as described above. The first filtrate had a pHvalue of 1.6 while the final washing water had a pH value of 3.05. Themoist catalyst substantially free from chloride was dried at 120° C. andactivity-tested in a hydrogenation reactor.

Example 18

Use of the catalyst of Example 17

355 g (corresponding to 1,000 ml) of the catalyst used in accordancewith Example 17 were activity-tested for 18 days in a 1 literhydrogenation reactor using a total of 389 l of raw materials, namely:

    ______________________________________                                        Tallow fatty acid methyl ester                                                                  IV = 50.2                                                                              SV = 199.5                                         Tallow fatty acid IV = 50  AV = 206.3                                         ______________________________________                                    

The following results were obtained:

    ______________________________________                                                     Total                                                                         throughput                                                                             T         LHSV                                          Raw material (l)      (°C.)                                                                            (l/h) IV                                      ______________________________________                                        Tallow fatty acid                                                                          38       170° C.                                                                          1     0.07                                    methyl ester 86       170° C.                                                                          1     0.06                                                 171      170° C.                                                                          2     0.48                                    Tallow fatty acid                                                                          197      190° C.                                                                          1     0.26                                                 256      190° C.                                                                          1     0.21                                                 328      200° C.                                                                          1     0.21                                                 389      200° C.                                                                          1     0.22                                    ______________________________________                                    

    ______________________________________                                        List of Reference Numerals                                                    ______________________________________                                        1               Fatty acid                                                    2               Receiver                                                      3               Heater                                                        4               Reactor                                                       5               High-pressure separator                                       6               Receiver                                                      7               Recycle gas compressor                                        8               Fresh hydrogen                                                ______________________________________                                    

We claim:
 1. In a process for the production of a shell catalystcontaining 0.3 to 5% by weight, based on the weight of the driedcatalyst, of palladium on an active carbon support by impregnating thesupport with an aqueous acidic palladium salt solution, precipitation ofpalladium and reduction of the palladium, the improvement whichcomprises: impregnating, a dry, alkaline, activated carbon having a pHvalue of at least 8, with the palladium salt solution, in the absence ofan oxidizing agent, and separating the carbon from the supernatantliquid after a pH of the supernatant liquid has increased from a pHbelow 1 to a pH of at least 1 whereby an outer shell comprisingpalladium is formed on the active carbon.
 2. The process of claim 1wherein the carbon is separated from the supernatant liquid after the pHof the supernatant liquid has increased to a pH of at least 1.6.
 3. Theprocess of claim 1 wherein the carbon is separated from the supernatantliquid after the pH of the supematant liquid has increased to a pH of atleast
 3. 4. The process of claim 1 wherein the carbon is separated fromthe supernatant liquid after the pH of the supematant liquid hasincreased to a pH of at least
 4. 5. The process of claim 1 wherein theactive carbon is agitated during impregnation with the palladium saltsolution.